It is well known to elevate bulk materials by entrapping the material between vertically oriented flights of belt conveyors which face one another. Generally it is known to trap the material in the elevating section between the belts by utilizing a compressible foam material placed to engage the rear faces of the belts. The compressibility of the foam material may be chosen to vary from edgge to edge and when less compressible adjacent the edges of the belts provides a force tending to urge the edges into sealing engagement with one another. In such arrangement, the density of the foam at the center of the belts is less than that at the edges. This arrangement has not proved entirely satisfactory.
It is also known to provide means whereby a fluid pressure is applied to the rear faces of the belts in the elevating section (see recently issued U.S. Pat. No. 3,762,534); however, this may not be entirely satisfactory because it has been found that unless higher pressures are applied to the edges to maintain them in contact with one another, material can readily escape at the belt edges.
According to this invention, there is provided a pair of endless, flexible, fluid impervious belts which have an elevating section in which the belts are in face-to-face relationship for transferring bulk material, such as relatively finely divided and granular material, between two levels. Thus, "when elevating section" is used, it is to apply equally to that part of the apparatus for transferring material from one level to another and higher level, or for transferring material from the higher level to the lower level. The elevating section of the apparatus can be substantially vertically arranged or at some inclination to the horizontal within the purview of the invention.
In any event, belt plenum chambers are arranged adjacent the backs of the belts in the elevating section, so that fluid pressure, preferably air, can be supplied to the belts in this section to urge them into engagement with the material therebetween. Also, to insure retention and substantially eliminate spillage from the edges, additional means, such as edge plenums, coextensive with the belt plenums, are provided. Fluid at a higher pressure than supplied to the belt plenums is supplied to these edge plenums. Thus forces are applied to the edges of the blets to urge them into engagement with one another and to maintain them in contact with one another.